Test your stack structure : TestCase « JUnit « Java Tutorial

1. Java Tutorial
2. JUnit
3. TestCase

import junit.framework.TestCase;

public class TestMyStack extends TestCase {

  public void testEmpty() throws Exception {
    MyStack stack = new MyStack();

    stack.checkInvariant();
    stack.push("sample");
    stack.checkInvariant();

    assertEquals("sample", stack.pop());
    stack.checkInvariant();

    stack.delete(1);
    stack.checkInvariant();
  }

}

class MyStack {
  public MyStack() {
    stack = new String[100];
    next_index = 0;
  }

  public String pop() {
    return stack[--next_index];
  }

  public void delete(int n) {
    next_index -= n;
  }

  public void push(String aString) {
    stack[next_index++] = aString;
  }

  public String top() {
    return stack[next_index - 1];
  }

  public void checkInvariant() throws Exception {
    if (!(next_index >= 0 && next_index < stack.length)) {
      throw new Exception("next_index out of range: " + next_index + " for stack length "
          + stack.length);
    }
  }

  private int next_index;

  private String[] stack;
}